The traditional access to PSTN is a copper wire network with an individual two wire copper line, referred to as access line or subscriber line, for each subscriber. The access line supports 3.1 kHz telephony and is terminated in a local office, or in a remote switch group. As a physical medium the copper pair can support much higher bandwidths, but traditional local offices can only support 64 kb/s, or multiples thereof, stream services. ISDN (Integrated Services Digital Network) is using the same type of copper line, but uses a DSL (Digital Subscriber Line) modulation technique, which provides 144 kb/s (2B+D). However, ISDN requires an entirely new network solution.
The traditional method to access Internet from a subscriber's home is to use a dialed up connection to a modem pool of an Internet server. The connection is set up in the PSTN. Over the connection information is exchanged in IP packets (packets using the Internet Protocol suit). At the subscriber's end of the access line a telephone and a PC (Personal Computer) is connected to a modem. The modem is used to provide for transmission of digital data. Due to restrictions posed by PSTN the bit rates at which the modem can transmit and receive data is limited to about 30 kb/s.
This known method to access Internet is slow, it takes up to 30 seconds to set up the connection. Once the connection is set up, its bandwidth is often utilized very poorly due to the bursty nature of the IP traffic. Also the transmission of large amounts of data, in particular graphic information such as a WWW page, is slow due to the limited bandwidth provided by the modem to modem connection on top of the digital 64 kb/s connection. Further, when the connection has been set up no incoming calls can be received and no outgoing calls can be placed.
From a network point of view the above method to access Internet has a serious problem. The PSTN network has been dimensioned by assuming certain characteristics of the traffic, among other things a certain mean value of the traffic on subscriber/access lines, and a certain mean value of the duration of calls. PSTN is a concentrating network, and the number of outgoing trunks from a local office may be as low as one fourth of the subscriber/access lines. Internet access via dialed up modem connections usually have a quite different traffic pattern. For example the duration of calls are much longer than the mean value for ordinary telephone calls, a fact that would call for redimensioning of the switched telephone network if Internet access over PSTN becomes very frequent.
Subscribers which have been provided ISDN can access Internet over one or two B-channels. If one B-channel is used for Internet access, the subscriber can still receive incoming telephone calls on the other. This known access method, however, has the same negative consequences for the network dimensioning as the dialed up modem method.
There is a rapid development on the copper access technology field. Compare ADSL Forum, General Introduction to Copper Access Technologies (Available at http.//www.adsl.com/general.sub.13 tutorial.html). A number of different modem technologies are being developed, such as VDSL (Very high bit rate Digital Subscriber Line) which provides 20 Mb/s in both directions over a copper pair up to a copper pair length of a few hundred meters. ADSL (Asymmetric Digital Subscriber Line) provides 1,5-9 Mb/s downstream and at least 16-640 kb/s upstream depending on the length of the copper pair length. However these technologies assume that the PSTN access should be provided as before and that a frequency band above the one used for PSTN access shall be used for data communication.
The recent development of the PSTN (ISDN) access network includes the standard interfaces V5.1 and V5.2 between local offices and access networks. These standards permit the introduction of access nodes which are connected to the local office.
Access nodes can also be connected to PSTN by a digital PABX (Private Automatic Branch Exchange) interface and to ISDN by a PRI (Primary Rate Interface). The V5 interfaces, the PRI interface and the PABX interface provide only 64 Kb/s bearer services and multiples thereof.
A previously known technique which permits simultaneously an Internet session and a telephony session over the same telephone access line includes a DSVD modem.(Digital Simultaneous transmission of Voice and Data on a single line).
A new technique that for simultaneously an Internet session and a telephony session over the same telephone access line includes a telephone doubler arrangement described in FIG. 1 below and in Swedish Patent Application No. 9602212-4.
The telephone doubler arrangement permits a user which is connected to an analogue telephone network to access an IP-based communication service and still be able to receive and answer incoming calls, and to place outgoing calls, while simultaneously surfing the Internet.
In FIG. 1 the telephone doubler arrangement 1 is shown to be connected to PSTN 2 and to Internet 3. At the user side a modem 4 is connected to PSTN 2, to a standard analogue telephone 5 and to a PC 6. The telephone doubler arrangement 1 comprises a modem pool 7 connected to PSTN 2, to Internet 3 and to a telephony server 9. The telephony server 9 is connected to PSTN 2.
When a user A is connected to Internet 3 via a dialed up PSTN connection to the modem pool 7 the telephone 5 cannot be used. On his/her PC the user can still communicate with other PSTN users by using the connectivity and multiplexing capabilities of IP. The dialed up line can carry a multiplexed stream of IP packages of: (a) an Internet session and (b) a telephony call. Speech carrying IP packages are routed to/from the telephony server 9 to PSTN. Telephony control signals are exchanged between the telephony server 9 and a telephony application 10 which runs on the PC. If the PC has audio capabilities, symbolized by a headset 11 comprising earphones and a microphone, a user A can be engaged in speech conversations with other users connected to the PSTN or ISDN. The user has got a new, soft phone on the PC 6.
Another new technique that allows for simultaneously an Internet session and a telephony session over the same telephone access line makes use of the telephone doubler principle described above complemented, at the user end, with an IP modem 12 as shown in FIG. 2 and in Swedish Patent Application No. 9604409-4. IP functionality, such as provided by the PC 6 in FIG. 1, has been integrated in the modem 12 and therefore the modem is referred to as an IP modem.
This arrangement makes possible a dialed up connection, using a standard analog telephone, or a telephony application on a PC, while simultaneously an Internet user is engaged in an Internet session over a PC connected to the same IP modem.
The arrangement shown in FIG. 2 is similar to that of FIG. 1. A telephone doubler arrangement 1 is connected to PSTN and Internet and comprises the same units as in FIG. 1.
Over a first IP link 13 between the IP modem and Internet 3 IP packets containing information relating to an Internet session are transported. Part of this link comprises a subscriber line 14 extending between the IP modem and PSTN. Over a second IP link 15 IP packets carrying digitized, compressed speech are transported to/from the telephony server and the modem pool. The telephony server creates a dynamic relation between the IP address of the IP modem and the telephone number of user A. Using the call forwarding service in PSTN incoming calls to user A are redirected to the telephony server.
The arrangement will allow user A to take and to place telephone calls using the ordinary telephone while there is an ongoing Internet session on the personal computer. Also a "soft phone" like the one in Swedish Appl. No. 9602212-4 is provided. Since the modem has IP capabilities it will be possible to communicate with other devices, such as an electricity consumption meter and similar devices, over a home network.
The IP modem is shown in FIG. 3 comprises a subscriber line interface 16, one or more telephone interfaces 17, 18, at least one PC interface 19 and, optionally, a LAN interface 20. There is also an IP multiplexor/demultiplexor 21 and a controller 22. An optional application 23 can run in the IP modem, such as for example an e-mail poller for polling electronic mail-boxes of user A. The IP multiplexor/demultiplexor routes IP packets from the subscriber line interface to their destinations; the PC, the telephone or the LAN. The controller provides control over the functionalities of the IP modem.
The Swedish patent applications cited above both provide telephony access and IP traffic can be superimposed the telephony access.
There are a number of problems related to access of traditional telephony and Internet over a traditional copper access line:
Neither the telephone doubler arrangement nor the DSVD modem solves the problem with the low utilization of a switched connection used as an access to Internet . Nor is the problem with many long-lasting Internet session over switched connections, which gives the PSTN network congestion, addressed.
Bandwidths above 64 kb/s on an analogue access line cannot be handled by traditional access methods. The V5 interface between local offices and access networks, and the PABX/PRI interfaces can only handle 64 kb/s channels. The use of the available bandwidth is bad since the multiplexing capabilities of IP cannot be used.
The telephone doubler arrangement and the DSVD modem requires speech compression on the access line, which introduces delays. Provided fax support is present in the telephone server the telephone doubler arrangement can be used to transfer fax messages.